In a conventional short message system, when a user equipment moves between a 2nd generation (2nd Generation, 2G) communications technology/3nd generation (3rd Generation, 3G) communications technology system and a Long Term Evolution (LTE, Long Term Evolution) system, the user equipment needs to perform location registration by means of a routing area update (RAU, Routing Area Update)/location area update (Location Area Update, LAU)/tracking area update (Tracking Area Update, TAU). For a mobile terminated short message (Mobile Terminated Short Message, MTSM) service, a home location register (Home Location Register, HLR)/home subscriber server (Home Subscriber Server, HSS) needs to return, according to registration information of the user equipment (user equipment, UE) in a mobile switching center (Mobile Switching Center, MSC)/visitor location register (Visitor Location Register, VLR) or a serving general packet radio service (General Packet Radio Service, GPRS) support node (Serving GPRS Support Node, SGSN) or a mobility management entity (Mobility Management Entity, MME), a correct address of a serving node to a gateway MSC for short message service (Gateway MSC For Short Message Service, SMS-GMSC), so that a short message is forwarded to the corresponding serving node and is sent to the user equipment.
A machine type communication (Machine Type Communication, MTC) application refers to network communication performed among one or more network elements or devices without human participation. Generally, the MTC application does not need voice communication, and data services are main demands of the MTC application. Currently, triggering by means of a short message is a main manner of Device Triggering in MTC. Different from the conventional short message system, two new network elements are defined in an MTC system, which are: a service capability server (Service Capability Server, SCS) and an MTC-interworking function (Machine Type Communication-InterWorking Function, MTC-IWF). The MTC-IWF may acquire, from an HSS, information (a name or an address of one or all of an MSC/VLR, an SGSN, and an MME) about a serving node that provides a short message service for a user, and send the information to a service center for short message service (Service Center for Short Message Service, SMS-SC), and then the SMS-SC sends a device triggering message to the user through the serving node.
A Validity-Period parameter indicating a validity period of a short message exists in a message for sending the short message, and indicates valid time of the short message starting from the time when the SMS-SC receives the short message, that is, time for which the SMS-SC needs to store the short message before the short message is successfully transmitted. In an MTSMS transmission process, if the short message cannot be transmitted or fails to be transmitted, the HLR/HSS adds a record to short message waiting data (Message Waiting Data, MWD) of a user, where the record includes an address of the SMS-SC serving the user. Subsequently, when the short message can be transmitted, the HLR/HSS instructs the SMS-SC to retransmit the short message to the user. However, for a short message whose value of Validity-Period is 0, the SMS-SC does not have data of the short message; therefore, even if the short message may be transmitted subsequently, the short message still cannot be retransmitted.